This invention relates to a novel synthetic crystalline material, to a method for its preparation and to its use in catalytic conversion of organic compounds.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. The zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat. No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is greater than 5 and up to infinity. U.S. Pat. No. 3,941,871 (U.S. Pat. No. Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe crystalline silicates or organosilicates of varying alumina and metal content.
Zeolite crystallization is a complex chemical problem (see Lok et al, ZEOLITES, 1983, Vol. 3, October, 282-291). An organic compound may or may not act as a zeolite synthesis directing agent. A single directing agent may lead crystallization to multiple structures and a single structure may be directed by different directing agents. The present crystalline material is shown herein to be directed from an appropriate reaction mixture by hexamethyleneimine. The only other uses of this organic as a zeolite directing agent known to applicant are in U.S. Pat. No. 4,439,409 for synthesis of PSH-3 and application Ser. No. 98,176, copending herewith, filed Sept. 18, 1987, now abandoned, for synthesis of another crystalline material. The present crystalline silicate has a novel structure and unique properties.